Factorial Designs: A Visual Approach No numbers! Research design explained

This tutorial is based on the example study described on page 467 of Research design explained.

In that study, all participants read 60 statements aloud. These statements were presented as a PowerPoint® slide show.

This tutorial is based on the example study described on page 467 of your text. In that study, all participants read 60 statements aloud. These statements were presented as a PowerPoint® slide show. However, not all slide shows were the same.

This tutorial is based on the example study described on page 467. In that study, all participants read 60 statements aloud. These statements were presented as a PowerPoint® slide show. However, not all slide shows were the same. Some slide shows presented negative statements (e.g., “I feel a little low today”), whereas other slide shows presented positive statements (e.g., “I feel pretty good today”). Thus, some participants read positive statements, whereas others read negative statements.

This tutorial is based on the example study described on page 420. In that study, all participants read 60 statements aloud. These statements were presented as a Powerpoint slide show. However, not all participants read the same 60 statements. Some read positive statements (e.g., “I feel pretty good today, though”), whereas others read negative statements (e.g., “However, I feel a little low today”). In addition, the slide shows varied in how fast they went. Some slide shows presented the statements at a fast rate; others presented the statements at a slow rate. Thus, some participants had to read and say the statements at a fast pace; the other participants did so at a slow pace.

Visually, we can diagram the design as follows: Participants Negative statements Positive statements Slow Fast

In short, participants saw one of four slide shows: 1.Slow paced, negative statements slide show, 2.Fast 2.Fast paced, negative statements slide show, 3.Slow paced, positive statements slide show, or a 4.Fast 4.Fast paced, positive statements slide show.

Thus, the experimenters varied two things: fast 1.Pace of the slide show (slow or fast) and 2.Type of statement (negative or positive).

For the purpose of this tutorial, imagine that participants rated their mood on the following scale. Unhappy Happy

Thus, a darker color represents a darker (less happy) mood, and a lighter color represents a lighter (more happy) mood. Unhappy Happy

As you can see from the next slide, this scale allows us to average participants responses without using numbers. Unhappy Happy

Color 1 Color 2 Average of Colors 1 & 2 (Black) (Black) (Black) (Gray) (Gray) (Gray) (White) (White) (White) (Black) (White) (Gray) (Black) (Gray) (Dark Gray)

Now, let’s look at some possible results.

Let’s start with the manipulations having no effect.

Suppose we observed no effect for any of the slide shows: Regardless of condition, everyone ended up in a good (light) mood. Slow speedFast speed Negative Statements Positive statements

Because type of statement does not matter, we could combine the results from the negative and positive statements, like this: Slow speedFast speed Negative statements and positive statements

Alternatively, because presentation speed does not matter, we could combine (collapse) the results from the slow and fast statements, like this: Slow and fast presentations Negative statements Positive statements

Finally, because neither presentation speed nor statement type matter, we could combine (collapse) the results into one box, like this: Slow and fast presentations Negative statements and positive statements

Suppose we observed no effect for any of the slide shows: Regardless of condition, everyone ended up in a bad (dark) mood. Slow speedFast speed Negative Statements Positive statements

Because type of statement does not matter, we could combine (collapse) the results from the negative and positive statements, like this: Slow speedFast speed Negative statements and positive statements

Alternatively, because presentation speed does not matter, we could collapse the results from the slow and fast statements, like this: Slow and fast presentations Negative statements Positive statements

Finally, because neither presentation speed nor statement type matter, we could combine (collapse) the results into one box, like this: Slow and fast presentations Negative statements and positive statements

Suppose we observed no effect for any of the slide shows: Regardless of condition, everyone ended up in a neutral (gray) mood. Slow speedFast speed Negative Statements Positive statements

Because type of statement does not matter, we could collapse the results from the negative and positive statements, like this: Slow speedFast speed Negative and positive statements

Alternatively, because presentation speed does not matter, we could collapse the results from the slow and fast statements, like this: Slow and fast presentations Negative statements Positive statements

Finally, because neither presentation speed nor statement type matter, we could combine (collapse) the results into one box, like this: Slow and fast presentations Negative and positive statements

In the next 3 slides, let’s look at the case in which positive statements help mood more than negative statements. This would be called a “statement main effect.”

A look at what the individual cells would look like if the only effect was that positive statements had a more positive effect on mood than negative statements. Slow speedFast speed Negative Statements Positive statements

A look at what the row averages would look like if the only effect was that positive statements had a more positive effect on mood than negative statements. Slow speedFast speedStatement Averages Negative Statements Positive statements Negative Positive On average, participants getting negative statements are in a darker mood than those getting positive statements, suggesting an effect for statement type.

A look at what the column averages would look like if the only effect was that positive statements had a more positive effect on mood than negative statements. Slow speedFast speedStatement Averages Negative Statements Positive statements Speed Averages Negative FastSlow Positive On average, participants getting the slow slide show are in the same mood than as getting the fast show, suggesting no effect for speed of presentation.

In the next 3 slides, let’s look at the case in which fast presentation of statements boosts mood more than slow presentation of statements. This would be called a “presentation speed main effect.”

A look at what the individual cells would look like if the only effect was that “fast” statements had a more positive effect on mood than “slow” statements. Slow speedFast speed Negative Statements Positive statements

Slow speedFast speed Negative Statements Positive statements Average of slow and fast speeds A look at what the column averages would look like if the only effect was that “fast” statements had a more positive effect on mood than “slow” statements. Slow Fast On average, participants getting the slow slide show are in the darker mood than those getting the fast show, suggesting an effect for speed of presentation.

Slow speedFast speed Average for negative and positive statements Negative Statements Positive statements Average of slow and fast speeds Another look at an experiment in which the only effect was a speed main effect. SlowFast Different Same Negative Positive

Slow speedFast speed Speed has the same effect for both positive and negative statements Positive Statements Negative Statements If there is only a speed main effect, we could collapse across the positive vs negative factor.

Interactions: Definition Now, let’s look at some interactions. In an interaction, a treatment’s effect in one condition is different from its effect in another condition.

Sometimes, interactions occur because a treatment has one effect in one condition, but the opposite effect in another condition. For example, some medications can have positive effects under certain circumstances, but negative effects under others. Let’s look at two examples of that.

Interaction Due to a Factor Having One Effect in One Condition and the Opposite Effect in Another Condition: Example 1 Slow speedFast speed Negative Statements Positive statements Mood lightens (+) Mood darkens (-) In this hypothetical example, speeding up the pace improves mood in the negative statements condition, but worsens mood in the positive statements condition.

Interaction Due to a Factor Having One Effect in One Condition and the Opposite Effect in Another Condition: Example 2 Slow speedFast speed Negative Statements Positive statements In this hypothetical example, speeding up the pace worsens mood in the negative statements condition, but improves mood in the positive statements condition. Mood lightens (+) Mood darkens (-)

Sometimes, interactions occur because a treatment has an effect in one condition, but no effect in another condition. Let’s look at four examples of this kind of interaction.

Interaction Due to a Factor Having One Effect in One Condition and No Effect in Another Condition: Example 1 Slow speedFast speed Negative Statements Positive statements Speeding up the pace has no effect on mood in the negative statements condition, but improves mood in the positive statements condition. Mood lightens (+) Mood does not change (0)

Interaction Due to a Factor Having One Effect in One Condition and No Effect in Another Condition: Example 2 Slow speedFast speed Negative Statements Positive statements Speeding up the pace has no effect on mood in the negative statements condition, but improves mood in the positive statements condition. Mood does not change (0) Mood lightens (+)

Interaction Due to a Factor Having One Effect in One Condition and No Effect in Another Condition: Example 3 Slow speedFast speed Negative Statements Positive statements Speeding up the pace has darkens mood in the negative statements condition, but has no effect on mood in the positive statements condition. Mood does not change (0) Mood darkens (-)

Interaction Due to a Factor Having One Effect in One Condition and No Effect in Another Condition: Example 4 Slow speedFast speed Negative Statements Positive statements Speeding up the pace has darkens mood in the negative statements condition, but has no effect on mood in the positive statements condition. Mood does not change (0) Mood darkens (-)

Sometimes, interactions occur because a treatment has more of an effect in one condition than in another. Let’s look at two examples of that.

Interaction due to a treatment has more of an effect in one condition than in another: Example 1 Slow speedFast speed Negative Statements Positive statements Speeding up the pace has lightens mood slightly in the negative statements condition, but lightens mood considerably in the positive statements condition. Mood lightens greatly (++) Mood lightens slightly (+)

Interaction due to a treatment has more of an effect in one condition than in another: Example 2 Slow speedFast speed Negative Statements Positive statements Speeding up the pace has darkens mood greatly in the negative statements condition, but darkens mood slightly in the positive statements condition. Mood darkens slightly (-) Mood darkens greatly (--)

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